He has been a Baby Beef, a beard rebel, an aircraftman and a guide to the Princes William and Harry as well as their mother, Princess Diana. He has also escorted the Obamas and the Putins to look at the Crown Jewels.

And if that was not enough, he also helps keep Thomas the Tank Engine on track.

Now after 20 years of life behind the ancient walls of the Tower of London, Chief Yeoman John Keohane is hanging up his uniform and ornate set of iron keys to all the state rooms.

John, 62, has become the longest-serving Chief Yeoman Warder at the Tower of London, after leaving the Royal Air Force to become a Baby Beef, the most junior recruit to the the Tower’s world-famous Beefeaters.

Having spend 20 years at the Tower, he is walking away, giving up his Georgian townhouse in the grounds and heading for Devon with his wife Ruth.

Devon is the county dearest to his heart, for it is the home of the South Devon Railway, where John plays the Fat Controller at the annual Thomas the Tank Engine convention.

National headlines

It is a role that brought him into conflict with Thomas fans and made national headlines when he refused to shave off his Beefeater’s beard to play the character.

He eventually caved in and had to take two weeks off for the beard to grow back before returning to the Tower.

John was made a member of the Royal Victorian Order in the Queen’s New Year Honours, and has escorted Her Majesty on hundreds of state occasions.

He says: “She is lovely. She puts you at ease, and once you have the formal introduction out of the way, she will just chat quite happily with you. She asks how the Tower is doing, but you only get a few minutes with her before she is moved on to meet other people.”

He was also the first to show Princes William and Harry the Crown Jewels when the Princess of Wales took them there as children.

“Diana was every bit of a mother,” John adds.

“She always wanted the best for her boys. But she was always friendly and it was very easy to forget who you were talking to.”

He has also met many heads of state, from Barack Obama to Vladimir Putin.

His home for the next couple of weeks will continue to be one of four Georgian townhouses, with two bedrooms and a cupboard, he jokes, and no gardens but rows of flowerpots.

The Beefeaters live in a community with its own bar – run by the Beefeater families themselves – chapel, doctor, gym, recreation grounds and bowling club.

John says: “We are a very close-knit team, and because we all come from very similar military backgrounds, we have a lot in common.

“We are no different to any other village. You get on with your neighbours, you make friends, you have long-term friends and some you put up with.”

In the morning John steps out of his blue front door and crosses the Tower’s Inner Ward to reach his office in the 12th-century Byward Tower.

“The best part is not having any travelling. I get up at seven, have a shower and breakfast. At quarter to eight I leave my house and at five to eight I’m sat at my desk.

“I oversee a body of 37 Yeoman staff, 36 male and one female. First I check we have the full complement of staff. If we have sickness we might need to move people into different positions. We have people responsible for security and people giving guided tours.”

He also has responsibility fortraining Beefeaters and ensuring they have the full uniform.

It takes four to six months to train a Yeoman, he says. “The history, what we call the Tower story, is very taxing to learn.”

Throughout the day John oversees four ceremonies – the opening of the Tower, the ceremony of the word – a military parade demonstrating to the public that a military garrison is based a the Tower, the closing ceremony and the nightly ceremony of the Keys when the Tower is locked up.

Ceremonial events

So what does he do when the formalities are out of the way?

“I deal with all the paperwork and emails and have various meetings with stakeholders.

“I’m responsible to the head of operations, Lt-Col John Brown, for organising ceremonial events such as the annual Ceremony of the Constable Dues that has just taken place.

“I also advise him on the Olympic Torch Relay, as the torch will spend its first night at the Tower, and the effects Games Lanes will have on traffic around here.”

In the evenings the Tower hosts corporate events, which John also oversees.

Throughout the year, he is responsible for occasions such as at Easter and Christmas – with state parades where Beefeaters are dressed in their fine regalia – and helps escort the Queen to the Beefeaters’ chapel.

“It’s been a real privilege to be part of this organisation and help people change their perception of the Tower. I shall miss it,” says John, who admits to being a bit nervous about leaving the Tower’s community behind.

For his retirement he has bought a house in Paignton. As a volunteer director of South Devon Railways, this takes him close to his fond hobby as the Fat Controller.

John says: “My grandchildren love finding photos of me as the Fat Controller on Facebook. I have a passion for the railways and the Routemaster bus we have down there, which I’ll drive for weddings and other occasions. I will also do some hill walking and spend time on the computer. I certainly won’t be bored.”